The present invention relates to controlling the cure rate of polymerizable or curable compositions that include a polymerizable component such as an ethylenically unsaturated compound. The invention is particularly useful for formulating adhesive compositions.
Curing is accomplished by activating a polymerization catalyst in the presence of a reactive component. Well known polymerization catalyst systems include aldehyde-amine condensation product systems and redox catalyst systems. A combination of these systems often is used to achieve cure. The present invention is especially useful for systems that at least include a free radical initiator or generator.
Most research efforts concerning such polymerization catalyst systems have been directed to accelerating rather than decelerating the rate of cure. However, end users of curable compositions such as adhesives have a need for slower curing products. If cure can be decelerated, this allows for a longer period of time for application and use of the curable composition after the polymerization catalyst has been activated, but before final cure has been achieved. In addition, it would be very useful to have a system in which the cure rate of a particular adhesive formulation could be adjusted easily during or after production.
A few approaches for slowing cure rate have been tried. For example, aldehyde-amine condensation products mentioned above and tertiary amines can be used as cure rate accelerators. One method for slowing the cure rate is to simply add a smaller amount of such accelerators. The problem with this approach is that the tendency of atmospheric oxygen to inhibit complete cure increases and the rate of cure of samples from the same batch or composition becomes erratic. A strong acid such as the reaction product of phosphorus pentoxide and 2-hydroxyethyl methacylate also can retard cure, but such material is expensive and the effect on cure rate is relatively small based on the amount of material added.
U.S. Pat. No. 3,725,504 relates to a 3 component adhesive that includes component A that is derived by partially polymerizing a mixture of polychloroprene, methylmethacrylate and styrene. Component A is then mixed with two other components to achieve the end product adhesive composition.
U.S. Pat. No. 3,832,274 relates to an adhesive that includes (A) 1-30 wt % of an elastomeric polymer, (B) 25-85 wt % of a polymerizable acrylic monomer, (C) 0-50 wt % of at least one ethylenically unsaturated non-acrylic monomer, (D) 0-60 wt % of a polymer derived from monomer (B) and/or (C), (E) 5-20 wt % of methacrylic acid and (F) 0.04-4 wt % of a reducing component of redox system. Styrene, chlorostyrene, vinyl toluene and vinyl acetate are listed in the specification as possible (C) monomers. Adhesive IVB described in Table XIII includes 5 pbw styrene and 15 pbw chlorostyrene.
U.S. Pat. No. 4,223,115 relates to a structural adhesive that can include the following possible free radical polymerizable components:
(1) a polymer-in-monomer syrup wherein the monomer can be a mixture of methyl methacrylate and styrene (see U.S. Pat. No. 3,725,504 above); PA1 (2) 10-90 wt % of at least one polymerizable material selected from a list wherein styrene and methyl methacrylate are included in the list, 10-90 wt % of at least one reaction product of isocyanate-functional prepolymer and hydroxy-functional monomer, 0.5-30 wt % (meth)acrylic acid, and 0-20 wt % of at least one polymerizable ethylenically unsaturated monomer; PA1 (3) the adhesive mixture disclosed in U.S. Pat. No. 3,832,274 above; PA1 (4) chlorosulfonated polyethylene and at least one polymerizable olefinically unsaturated monomer; or PA1 (5) 25-95 wt % of at least one alkyl ester or hydroxy alkyl ester of (meth)acrylic acid, and 5-75 wt % of polyvinyl alkyl ether, styrene-acrylonitrile resin or unsaturated polyester resin. PA1 (a) 10-90, preferably 20-70, weight percent of an ethylenically unsaturated monomer selected from the group consisting of (meth)acrylic acid; esters, amides or nitrites of meth)acrylic acid; maleate esters; fumarate esters; vinyl esters; conjugated dienes; itaconic acid and esters thereof; and vinylidene halides; PA1 (b) 10-80, preferably 20-50, weight percent of a diene-based elastomer; PA1 (c) 0-40, preferably 1-25, weight percent of an olefinic urethane reaction product of an isocyanate-functional prepolymer and a hydroxy-functional monomer having at least one unit of polymerizable unsaturation, such reaction product being characterized by the presence of at least two units of unsaturation and the substantial absence of free isocyanate products; PA1 (d) 0-20, preferably 2-10, weight percent of a phosphorus-containing compound having one or more olefinic groups and no less than one P--OH group; PA1 (e) an ambient temperature-active catalyst system that includes at least one reducing agent and at least one oxidizing agent that are co-reactive at ambient temperature to generate free radicals that are capable of initiating and propagating the cure of said adhesive composition; and PA1 (f) less than 5 weight percent of the vinyl aromatic compound, wherein the weight percents are based on the total weight of components (a)-(f). PA1 (I) a first package comprising PA1 (II) a second package comprising PA1 wherein the weight percents are based on the total amount of the first package. PA1 (1) from about 0.5 to about 50 percent by weight, based on total weight of bonding activator, of at least one oxidizing agent which can function as an oxidant of a redox couple catalyst system; and PA1 (2) from about 30 to about 99.5 percent by weight, based on total weight of bonding activator, of a carrier vehicle. In addition, the bonding activator also can contain either the epoxy component or the phosphorus-containing compound.
Styrene, vinyl styrene and methylstyrene are included in the list of possible olefinically unsaturated compounds for classes (1), (2), (3) and (4), but there does not appear to be any example in the patent wherein any of these compounds are present as a distinct or separate component of the end product adhesive formulation.